DDNFS: a Distributed Digital Notary File System

Abstract

Safeguarding online communications using public key cryptography is a well-established practice today, but with the increasing reliance on `faceless', solely online entities one of the core aspects of public key cryptography is becoming a substantial problem in practice: Who can we trust to introduce us to and vouch for some online party whose public key we see for the first time? Most existing certification models lack flexibility and have come under attack repeatedly in recent years, and finding practical improvements has a high priority. We propose that the real-world concept of a notary or certifying witness can be adapted to today's online environment quite easily, and that such a system when combined with peer-to-peer technologies for defense in depth is a viable alternative to monolithic trust infrastructures. Instead of trusting assurances from a single party, integrity certifications (and data replication) can be provided among a group of independent parties in a peer-to-peer fashion. As the likelihood of all such assurance providers being subverted at the very same time is very much less than that of a single party, overall robustness is improved. This paper presents the design and the implementation of our prototype online notary system where independent computer notaries provide integrity certification and highly-available replicated storage, and discusses how this online notary system handles some common threat patterns.